Four patients with gyrate atrophy of the choroid and retina, with hyperornithinemia, and ornithine keto-acid amino transferase deficiency are being followed on treatment with oral vitamin B6. Three of the four have shown significant reduction of the elevated serum ornithine and return to normal of the depressed serum lysine which is characteristic of the disease. Two of the three responsive patients were studied both on and off vitamin B6 treatment - both showed improvement of electroretinography and electro-oculography when treated and decreased electroretinographic responses when supplemental B6 was discontinued. The significance of these and other clinical changes will be investigated further. In vitro response to B6 was studied in cultured skin fibroblasts in controls, patients, and obligate heterozygotes. Further studies on carrier detection and biochemicaL characterization are in progress.